class Solution {
    public int peakIndexInMountainArray(int[] arr) {
        int left=0,right=arr.length-1;
        while(left<right){
            int mid=left+(right-left+1)/2;
            if(arr[mid]<arr[mid-1]) right=mid-1;
            else left=mid;
        }
        return right;
    }
}